ABSTRACTThis study selectively acylated the primary hydroxyl groups on flavonoids in antioxidant of bamboo leaves (AOB) using lauric acid with Candida antarctica lipase B in tert-amyl-alcohol. The separation and isolation of acylated derivatives were performed using silica gel column chromatography with a mixture of dichloromethane/diethyl ether/methanol as eluents. Both thin layer chromatography and high-performance liquid chromatography analyses confirmed the high efficiency of the isolation process with the purified orientin-6″-laurate, isoorientin-6″-laurate, vitexin-6″-laurate, and isovitexin-6″-laurate that were obtained. The addition of AOB and acylated AOB reduced acrylamide formation in fried potato crisps. Results showed that 0.05% AOB and 0.05% and 0.1% acylated AOB groups significantly (p < 0.05) reduced the content of acrylamide in potato crisps by 30.7%, 44.5%, and 46.9%, respectively.

Mentions:
HPLC analyses confirmed that the liquid/liquid extraction step was not sufficient to separate AOB or the acylated derivatives, as both components were found at high levels (Fig 3A). Fig 3B shows that the content of residual flavonoids was much lower after filtration through silica gel. Previous studies have discussed the preparative isolation of orientin, isoorientin, vitexin, and isoorientin from plant extracts using the preparative HPLC method. For example, Zhang et al. established the simultaneous purification and isolation of flavonoids in bamboo leaf extracts using AB-8 resin-based column chromatography followed by preparative HPLC using a mobile phase consisting of 10% and 15% (v/v) of acetonitrile and 1% acetic acid in water [14]. Similarly, the separation and isolation of flavonoid esters can be performed on preparative HPLC. Ardhaoui et al. performed the separation of quercetin, hesperidin, rutin and esculin fatty acids esters directly through preparative HPLC using a methanol/acetic acid solution (water/acetic acid, 97:3, v/v)(at 0 min (30:70, v/v), 5 min (100:0, v:v), 10 min (100:0, v:v), 15 min (30:70, v/v)) [22]. In this study, the possibility of using the preparative HPLC method were investigated, but it was not sufficient to purify these isomers with extremely similar polarities. Fig 4 shows a slight differentiation of isomer pairs of isoorientin/orientin-6″-laurate and isovitexin/vitexin-6″-laurate. Silica gel column chromatography has also been used in the purification of flavonoids and flavonoid esters. Afifi et al. separated isoorientin from Arum palaestinum by silica gel column chromatography [28], and Kontogianni et al. purified naringin esters by column chromatography on silica gel (their products were eluted with acetonitrile/methanol/water (8:2:0.3, v/v/v)) [29]. In our study, the TLC analyses were performed with a mixture of dichloromethane/diethyl ether/methanol (65:30:5, v/v/v) as eluents, and clear spots without overlapping were obtained (Fig 5). Accordingly, the isolation of AOB acylated derivatives was performed on a silica gel column using the same eluents (dichloromethane/diethyl ether/methanol, 80:15:5, v/v/v). The isolated products were reanalyzed by HPLC (Fig 6), which confirmed that adequate separation was achieved by silica gel column chromatography. From these results, it can be concluded that in comparison with the preparative HPLC method, silica gel column chromatography is more efficient, convenient, and economical for the separation of AOB acylated derivatives.

Mentions:
HPLC analyses confirmed that the liquid/liquid extraction step was not sufficient to separate AOB or the acylated derivatives, as both components were found at high levels (Fig 3A). Fig 3B shows that the content of residual flavonoids was much lower after filtration through silica gel. Previous studies have discussed the preparative isolation of orientin, isoorientin, vitexin, and isoorientin from plant extracts using the preparative HPLC method. For example, Zhang et al. established the simultaneous purification and isolation of flavonoids in bamboo leaf extracts using AB-8 resin-based column chromatography followed by preparative HPLC using a mobile phase consisting of 10% and 15% (v/v) of acetonitrile and 1% acetic acid in water [14]. Similarly, the separation and isolation of flavonoid esters can be performed on preparative HPLC. Ardhaoui et al. performed the separation of quercetin, hesperidin, rutin and esculin fatty acids esters directly through preparative HPLC using a methanol/acetic acid solution (water/acetic acid, 97:3, v/v)(at 0 min (30:70, v/v), 5 min (100:0, v:v), 10 min (100:0, v:v), 15 min (30:70, v/v)) [22]. In this study, the possibility of using the preparative HPLC method were investigated, but it was not sufficient to purify these isomers with extremely similar polarities. Fig 4 shows a slight differentiation of isomer pairs of isoorientin/orientin-6″-laurate and isovitexin/vitexin-6″-laurate. Silica gel column chromatography has also been used in the purification of flavonoids and flavonoid esters. Afifi et al. separated isoorientin from Arum palaestinum by silica gel column chromatography [28], and Kontogianni et al. purified naringin esters by column chromatography on silica gel (their products were eluted with acetonitrile/methanol/water (8:2:0.3, v/v/v)) [29]. In our study, the TLC analyses were performed with a mixture of dichloromethane/diethyl ether/methanol (65:30:5, v/v/v) as eluents, and clear spots without overlapping were obtained (Fig 5). Accordingly, the isolation of AOB acylated derivatives was performed on a silica gel column using the same eluents (dichloromethane/diethyl ether/methanol, 80:15:5, v/v/v). The isolated products were reanalyzed by HPLC (Fig 6), which confirmed that adequate separation was achieved by silica gel column chromatography. From these results, it can be concluded that in comparison with the preparative HPLC method, silica gel column chromatography is more efficient, convenient, and economical for the separation of AOB acylated derivatives.

Bottom Line:
Both thin layer chromatography and high-performance liquid chromatography analyses confirmed the high efficiency of the isolation process with the purified orientin-6″-laurate, isoorientin-6″-laurate, vitexin-6″-laurate, and isovitexin-6″-laurate that were obtained.The addition of AOB and acylated AOB reduced acrylamide formation in fried potato crisps.Results showed that 0.05% AOB and 0.05% and 0.1% acylated AOB groups significantly (p < 0.05) reduced the content of acrylamide in potato crisps by 30.7%, 44.5%, and 46.9%, respectively.

ABSTRACTThis study selectively acylated the primary hydroxyl groups on flavonoids in antioxidant of bamboo leaves (AOB) using lauric acid with Candida antarctica lipase B in tert-amyl-alcohol. The separation and isolation of acylated derivatives were performed using silica gel column chromatography with a mixture of dichloromethane/diethyl ether/methanol as eluents. Both thin layer chromatography and high-performance liquid chromatography analyses confirmed the high efficiency of the isolation process with the purified orientin-6″-laurate, isoorientin-6″-laurate, vitexin-6″-laurate, and isovitexin-6″-laurate that were obtained. The addition of AOB and acylated AOB reduced acrylamide formation in fried potato crisps. Results showed that 0.05% AOB and 0.05% and 0.1% acylated AOB groups significantly (p < 0.05) reduced the content of acrylamide in potato crisps by 30.7%, 44.5%, and 46.9%, respectively.